At present, a sulfonylurea, a biguanide, an α-glucosidase inhibitor and the like have been used as agents for treating diabetes. While a sulfonylurea produces a potent hypoglycemic action, it sometimes causes serious hypoglycemia and requires attention during use. A biguanide easily causes relatively serious lactic acidosis as a side effect. An α-glucosidase inhibitor delays digestion and absorption of glucose in the gastrointestinal tract and suppresses increase in the blood glucose level after meal, but side effects of sense of distension, diarrhea and the like are problematic (JOSLIN'S DIABETES MELLITUS 13Th Edition 521–522).
As isoxazole derivatives, for example, the following compounds are known.    (1) JP-B-44-29656 describes that a compound represented by the formula
    wherein R is a phenyl group, R′ is a hydrogen or a lower alkyl group, A is a straight-chain or branched divalent hydrocarbon group having 2 to 5 carbon atoms, and Q′ is a hydroxy group, an amino group or an acylamino group, has an analgesic action, an antitussive action, an antipyretic action and an anti-inflammatory action.    (2) Japanese Patent Application under PCT laid-open under kohyo No. 9-509951 describes that a compound represented by the formula
    wherein one of R1 and R2 is 3,5-dimethyl-4-hydroxyphenyl and the other R1 or R2 is pyridyl etc.; A is a double bond etc.; R4 is a hydrogen atom etc.; and R3 is a hydrogen atom, (C1–C4)-alkyl or hydroxy-(C1–C4)-alkyl, is useful for the treatment of inflammation, asthma, rheumatic disease and autoimmune disease.    (3) WO00/08001 describes that a compound represented by the formula
    wherein R1 and R3 are each an optionally substituted lower alkyl, aryl etc., and R2 is a hydrogen atom etc., is useful as an estrogen receptor modulator.    (4) WO98/28282 describes that a compound represented by the formula
    wherein ring M may contain 0 to 2 N-atoms besides J; J is O or S; D is CN etc.; E is phenyl etc.; G is absent or NHCH2 etc.; Z is C1-4 alkylene etc.; R1a and R1b are independently absent or —(CH2)r—R1′ (r is 0, 1, 2 or 3, R1′ is hydrogen atom etc.) etc.; A is C3-10 carbocyclic residue etc.; B is C3-10 carbocycle residue etc.; s is 0, 1 or 2, is useful as a Xa factor inhibitor.
However, it is not known that the above-mentioned isoxazole derivatives are useful as agents for the prophylaxis or treatment of diabetes or impaired glucose tolerance, insulin secretagogues and the like.